Sprinkle a pinch of mozzarella cheese in a thin line parallel to the shortest edge of each triangle, ensuring the cheese doesn't touch the edges. Top the mozzarella cheese with Parmesan cheese and parsley flakes.

Roll the short end of each triangle halfway toward the top point, creating a rim, and sprinkle garlic powder over dough. Place a mushroom half on half of the triangles, midway between the rim and the top point, and a pepperoni half in the same place on the remaining triangles. Place 1 or 2 olive slivers against the rim to form a "ribbon" or "belt" on each "hat". Place the "hats" on the prepared baking sheets.